Examination of the ground scars and photographs taken before the wreckage was moved revealed a wreckage distribution pattern associated with a condition of high deceleration forces and a steep angle of descent to the level ground, which is consistent with a loss of control. Weather, pilot incapacitation, and engine failure were assessed as unlikely contributors; the investigation focussed on flight control malfunction/failure. The observations made during testing with the Bell 206B static display demonstrated that damage around the main transmission was consistent with the misalignment of the pylon assembly in flight. Although the main driveshaft and the pylon assembly were misaligned, the main rotor and tail rotor were still being driven by the engine until the time of impact. The right-hand pylon support spindle was found fractured at the root end of the journal section, yet the spherical bearing supporting the spindle did not display impact-related damage. This indicates that the right-hand pylon support spindle was not in the spherical bearing at the time of impact. A fatigue fracture is not consistent with an impact force. The dimensional restoration repair of the spindle journal introduced a stress concentration feature at the location of the subsurface radius, which was responsible for the formation of the fatigue crack and subsequent failure of the right-hand pylon support spindle. Testing with the Bell 206B static aircraft also demonstrated that the cyclic and collective control linkages could partially support the fuselage from the swash plate assembly, and this condition would render the helicopter uncontrollable in flight, regardless of pilot inputs. It is likely that the time between the spindle failure and ground impact could be measured in seconds. If the helicopter had flown for any longer, any uncontrolled gyrations that may have occurred would likely have resulted in the helicopter breaking apart in flight. Since the accident site was compact, it is more likely that the helicopter was at a low altitude and collided with the ground before time allowed it to break up in flight. While it is beyond the scope of this investigation to determine the adequacy or appropriateness of engineering practices, the differing assessment, by different individuals, of whether the spindles were exposed to dynamic loads or static loads introduced risk. The design process for the repair of a critical part was approved, likely without the benefit of all original design data. It could not be shown that tests, stress analyses or other techniques were used in lieu of these data to ensure that the repaired part maintained the strength and other properties assumed in the original design. As the authority to approve repairs, TC must ensure that it, or its delegates, can demonstrate that approved repairs of critical parts do not compromise the required level of integrity. The following TSB Engineering Laboratory report was completed: LP 010/2007 - Main Transmission Spindle Fracture This report is available from the Transportation Safety Board of Canada upon request.Analysis Examination of the ground scars and photographs taken before the wreckage was moved revealed a wreckage distribution pattern associated with a condition of high deceleration forces and a steep angle of descent to the level ground, which is consistent with a loss of control. Weather, pilot incapacitation, and engine failure were assessed as unlikely contributors; the investigation focussed on flight control malfunction/failure. The observations made during testing with the Bell 206B static display demonstrated that damage around the main transmission was consistent with the misalignment of the pylon assembly in flight. Although the main driveshaft and the pylon assembly were misaligned, the main rotor and tail rotor were still being driven by the engine until the time of impact. The right-hand pylon support spindle was found fractured at the root end of the journal section, yet the spherical bearing supporting the spindle did not display impact-related damage. This indicates that the right-hand pylon support spindle was not in the spherical bearing at the time of impact. A fatigue fracture is not consistent with an impact force. The dimensional restoration repair of the spindle journal introduced a stress concentration feature at the location of the subsurface radius, which was responsible for the formation of the fatigue crack and subsequent failure of the right-hand pylon support spindle. Testing with the Bell 206B static aircraft also demonstrated that the cyclic and collective control linkages could partially support the fuselage from the swash plate assembly, and this condition would render the helicopter uncontrollable in flight, regardless of pilot inputs. It is likely that the time between the spindle failure and ground impact could be measured in seconds. If the helicopter had flown for any longer, any uncontrolled gyrations that may have occurred would likely have resulted in the helicopter breaking apart in flight. Since the accident site was compact, it is more likely that the helicopter was at a low altitude and collided with the ground before time allowed it to break up in flight. While it is beyond the scope of this investigation to determine the adequacy or appropriateness of engineering practices, the differing assessment, by different individuals, of whether the spindles were exposed to dynamic loads or static loads introduced risk. The design process for the repair of a critical part was approved, likely without the benefit of all original design data. It could not be shown that tests, stress analyses or other techniques were used in lieu of these data to ensure that the repaired part maintained the strength and other properties assumed in the original design. As the authority to approve repairs, TC must ensure that it, or its delegates, can demonstrate that approved repairs of critical parts do not compromise the required level of integrity. The following TSB Engineering Laboratory report was completed: LP 010/2007 - Main Transmission Spindle Fracture This report is available from the Transportation Safety Board of Canada upon request. The dimensional restoration repair of the spindle journal introduced a stress concentration feature at the location of the subsurface radius, which was responsible for the formation of the fatigue crack and subsequent failure of the right-hand pylon support spindle. Failure of the right-hand pylon support spindle in flight caused the helicopter to become uncontrollable and collide with the level ground.Findings as to Causes and Contributing Factors The dimensional restoration repair of the spindle journal introduced a stress concentration feature at the location of the subsurface radius, which was responsible for the formation of the fatigue crack and subsequent failure of the right-hand pylon support spindle. Failure of the right-hand pylon support spindle in flight caused the helicopter to become uncontrollable and collide with the level ground. It is likely that the pylon support spindle repair process was designed without the benefit of all original design data. It could not be shown that tests, stress analyses or other techniques were used to ensure that the repair maintained the strength and other properties assumed in the original design data. There is a risk that repair designs for parts identified as critical parts may have been approved before the definition of critical parts, applicable to normal category rotorcraft, was adopted by Transport Canada. Such repair schemes may not ensure that critical parts maintain the critical characteristics on which certification is based. Transport Canada made inquiries regarding approved spindle repair procedures following the release of Bell Helicopter Textron Inc. Operational Safety Notice206-99-35 RevisionA, but closed the file without formally reviewing or cancelling the two approved repair certificates, thus allowing the repair to continue in its original form.Findings as to Risk It is likely that the pylon support spindle repair process was designed without the benefit of all original design data. It could not be shown that tests, stress analyses or other techniques were used to ensure that the repair maintained the strength and other properties assumed in the original design data. There is a risk that repair designs for parts identified as critical parts may have been approved before the definition of critical parts, applicable to normal category rotorcraft, was adopted by Transport Canada. Such repair schemes may not ensure that critical parts maintain the critical characteristics on which certification is based. Transport Canada made inquiries regarding approved spindle repair procedures following the release of Bell Helicopter Textron Inc. Operational Safety Notice206-99-35 RevisionA, but closed the file without formally reviewing or cancelling the two approved repair certificates, thus allowing the repair to continue in its original form. On 06 February 2007, the TSB issued Occurrence Bulletin OB-A06P0190-1 addressed to Transport Canada (TC). The Occurrence Bulletin provided a factual description of the failure mode of the pylon support spindle. On 27 February 2007, TC issued Airworthiness Directive (AD) CF-2007-02, which mandated removal of all Bell206B pylon support spindles that had been repaired by Cadorath Aerospace Inc. and mandated that maintenance records be annotated accordingly. On 09 March 2007, Bell Helicopter Textron Inc. (BHTI) issued Operational Safety Notice (OSN)206-99-35 RevisionB. This document is a revision of the previous version (RevisionA) and reinforces BHTI's opposition to dimensional restoration repairs of Bell206B pylon support spindles. On 23 August 2007, AD CF-2007-02 was superseded and CF-2007-02R1 was issued by TC. The revision included serial numbers of pylon support spindles, which incorporated a similar repair performed by H-STool Parts Inc. TC is in the process of withdrawing both of the identified Repair Design Certificates and Repair Authority for the Bell206 pylon support spindles, issued by a TC delegate, to Cadorath Aerospace Inc. and H-STool Parts Inc. On 06 November 2007, AD 2007- 22-01 issued by the United States Federal Aviation Administration became effective. This AD reflected the concerns and part serial numbers stated in AD2007-02R1 issued by TC and required that all affected spindles be removed from service within 16hours of time in service.Safety Action Taken On 06 February 2007, the TSB issued Occurrence Bulletin OB-A06P0190-1 addressed to Transport Canada (TC). The Occurrence Bulletin provided a factual description of the failure mode of the pylon support spindle. On 27 February 2007, TC issued Airworthiness Directive (AD) CF-2007-02, which mandated removal of all Bell206B pylon support spindles that had been repaired by Cadorath Aerospace Inc. and mandated that maintenance records be annotated accordingly. On 09 March 2007, Bell Helicopter Textron Inc. (BHTI) issued Operational Safety Notice (OSN)206-99-35 RevisionB. This document is a revision of the previous version (RevisionA) and reinforces BHTI's opposition to dimensional restoration repairs of Bell206B pylon support spindles. On 23 August 2007, AD CF-2007-02 was superseded and CF-2007-02R1 was issued by TC. The revision included serial numbers of pylon support spindles, which incorporated a similar repair performed by H-STool Parts Inc. TC is in the process of withdrawing both of the identified Repair Design Certificates and Repair Authority for the Bell206 pylon support spindles, issued by a TC delegate, to Cadorath Aerospace Inc. and H-STool Parts Inc. On 06 November 2007, AD 2007- 22-01 issued by the United States Federal Aviation Administration became effective. This AD reflected the concerns and part serial numbers stated in AD2007-02R1 issued by TC and required that all affected spindles be removed from service within 16hours of time in service.